In the previous section, some of the calculated values of EP coupling strength \(\lambda \)  for the verified hydrides have been mentioned. The sample is small, but it has already been clear that \(\lambda \)  in itself is a poor indicator of T\(_c\) ; increasing \(\lambda \)  should not be the primary goal. Indications from Allen-Dynes analysis[1]} through more recent studies[2]} indicate that increasing the electron-proton scattering matrix element should become the focus of attention. Practically nothing is understood at present about what keeps \(I^2\)  large in the RTS materials when the electron gas is being compressed to higher density, and (in the simplest picture) should be screening more strongly, and reducing \(I^2\) . \(N(0)\)  itself is usually normal in size, which may help to promote stability. Several groups have noted that the H-atom DOS \(N_H(0)\)  per unit volume is likely to be the relevant quantity, but does not correlate strongly with T\(_c\) .
